The overall objectives of the project are to develop GC/MS techniques for 1) profiling the urinary excretion of modified nucleosides in patients with various neoplasms; 2) determination of the urinary excretion levels of 2'-O-methylated nucleosides of normal patients and patients with cancer; 3) studying the metabolism and to quantitate the distribution and excretion of psi ox, the periodate oxidation product of pseudouridine, in the urine and tissues of mice; 4) and develop methods for the incorporation of stable isotopes into nucleosides. Development of the synthetic methods for incorporation of stable isotopes into nucleic acid analogs could have a significant effect on studies involving the metabolism, distribution and excretion of medicinally important nucleic acid bases, nucleosides and nucleotides. Coupled with gas chromatography-mass spectrometry, results of the techniques outlined in this proposal could have an influence in designing dosage regimens for treating cancer and viral infection and aid in the synthesis of more effective antitumor and anti-viral drugs.